What are the advanced React Native interview questions and answers?
React Native is a widely-used mobile development framework that allows developers to create mobile apps for Android and iOS using JavaScript. In just a few years, it has become a leading choice for mobile app development, with notable examples being Instagram, Facebook, and Skype.
If you want to land that React Native developer job of your dreams, you need to be well-prepared for your next interview with a top-notch resume on hand. We’ve prepared some of the most frequently asked React Native interview questions for experienced developers with sample answers to help you ace your interview 👇🏼
10 Advanced React Native Interview Questions and Answers
1. What’s the main cause of the performance issues in React Native?
The performance issues in React Native are caused by the immense speed of each thread (i.e. JS and Native thread). Bottlenecks in React Native apps generally occur when components from one thread are being passed onto another more than required. To avoid this kind of issues, it’s crucial to keep the passes over the bridge to a minimum.
2. Memory leaks in React Native: describe what they are, including their main causes, and how they can be detected.
Memory in JavaScript is managed automatically by the Garbage Collector, which is responsible for monitoring memory allocation (allocated objects and their references) and determining whether a certain block of allocated memory is no longer needed and, thus, cleaning it up. When it encounters a part of the graph that is not being referenced indirectly or directly from the root objects, that part might be completely deallocated from the memory.
Such memory leaks can be prevented.
Remember, in React Native each JavaScript module is attached to a root object. Many modules (including the React Native core modules) declare variables that are kept in the main scope (e.g. when an object outside of a function or class is defined in a JavaScript module). Because of those variables, other objects can be retained and prevented from being labeled as ‘garbage’ by the algorithm.
Common mistakes that lead to memory leaks in React Native apps include:
- Closure scope leaks
- Unreleased listeners/timers added in componentDidMount
Here’s how you can detect memory leaks for iOS and Android:
|
iOS |
Android |
|
· In Xcode, · After that it will show you all templates. Click on ‘Leaks’ and proceed with ‘Choose’.
|
· Run React Native app normally (react-native run-android) · Run Android Studio · On the menu, · Click Tools → Android → Android Device Monitor · When Android Device Monitor shows up, click Monitor → Preferences |
3. What is FlatList, and how is it better than ScrollView?
In React Native, the FlatList component is used to present large amounts of data in a scrolling list format. This is commonly used in apps like news apps, where a list of article summary cards are displayed on the home page. It is more suitable for lists of data that may change over time, unlike ScrollView. The FlatList component only renders items that are visible on the screen, providing a performance boost as it only creates the cards when the user starts scrolling, unlike ScrollView which creates all the list items at once.
4. What is SSL Pinning in React Native?
SSL pinning (or certificate pinning) is a technique used to enhance the security of SSL/TLS connections by linking a certificate or public key to a specific host. This helps to prevent man-in-the-middle (MITM) attacks, in which an attacker intercepts and alters SSL/TLS traffic, by ensuring that the certificate or public key used to establish the connection is the one that is expected.
5. What is a controlled and uncontrolled component in React Native?
React Native components can be divided into two categories based on their internal state. Some components, such as textInput, have a value attribute that is used to display user input on the UI. These are considered uncontrolled components because React is not responsible for setting or changing their value.
However, if the state of a component is managed by React, it is considered a controlled component. To make a component controlled, the developer assigns the component’s state as the value of control elements and adds a callback method to update the state on value change events. It is recommended to use controlled components in React Native as it allows for better management of values and behavior by React and gives the developer more control over the state of components.
6. What is rendering prop pattern in React Native?
The rendering prop pattern is a technique in React and React Native for sharing logic between components. It allows a component (often referred to as the “container” or “higher-order” component) to pass a function that defines the markup to be rendered as a prop to another component (often referred to as the “child” or “presentational” component). The child component then calls this function, passing in any props that it receives, to render the markup.
The main advantage of this pattern is that it allows for greater flexibility and reusability. The container component can handle the logic and state management, while the child component can focus solely on rendering the markup. This also allows for the child component to be used in multiple contexts with different logic and state.
7. How does virtual DOM work in React Native?
The virtual DOM (Document Object Model) is a mechanism used by React to efficiently update the user interface (UI) of a web or mobile application. The virtual DOM is a representation of the actual DOM, and it allows React to compare the current state of the UI with the desired state, and then make only the necessary changes to the actual DOM.
When a component’s state or props change, React will first update the virtual DOM to reflect the new state. It will then compare the virtual DOM with the previous version of the virtual DOM, and calculate the minimal set of changes required to update the actual DOM. This process is called reconciliation.
Once the minimal set of changes has been calculated, the virtual DOM updates the native views that are used to render the UI. This allows React Native to efficiently update the UI of a mobile app while still taking advantage of the performance benefits of native code.
8. What are some the core components in React Native? Name the analogies of those components in web development.
There are several core components in React Native that are used to build the user interface of a mobile app. Some of the most commonly used components include:
|
React Native Component |
Web Analog |
Description |
|
<Text> |
<p> |
Displays, styles, and nests strings of text and even handles touch events |
|
<View> |
A non-scrolling <div> |
Groups other components together and applies styles |
|
<Image> |
<img> |
Displays images |
|
<ScrollView> |
<div> |
A generic scrolling container that can contain multiple components and views |
|
<TextInput> |
<input type=“text”> |
Creates text input fields |
9. What is setNativeProps?
setNativeProps is a method available in React Native that allows you to directly update the properties of a component’s corresponding native view. This can be useful in certain situations where you need to update the view without triggering a full re-render of the component.
Normally, when you update the state or props of a component, React will re-render the component and its children to reflect the new state. This can be slow and wasteful if you only need to make small updates to the view. By using setNativeProps, you can bypass the re-rendering process and update the native view directly, which can improve performance.
It’s worth noting that setNativeProps should be used sparingly and with caution, as it bypasses the normal react reconciliation process and it could cause unexpected behavior if not used correctly. You should only use setNativeProps when you are certain that it will result in better performance and it won’t cause any inconsistencies.
10. What is the difference between FlatList and SectionList?
FlatList and SectionList are both components in React Native that allow for rendering large lists of data efficiently.
FlatList is a component for efficiently rendering large lists of items in a scrollable view. It renders items lazily, meaning that it only renders the items that are currently visible on the screen, and unmounts items that are no longer visible.
SectionList is similar to FlatList, but it allows you to group items into sections. Each section can have a header and footer, and the items in the section are rendered using a FlatList.
In summary, FlatList is used to render a simple list of items, whereas SectionList is used to render a list of items grouped into sections.
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